(1) Field of the Invention
The present invention generally relates to a malfunction detection apparatus, and more particularly to an apparatus for detecting a malfunction in an evaporated fuel purge system which is provided in an internal combustion engine for purging evaporated fuel, or fuel vapor, into an intake system of the internal combustion engine under given operating conditions and for adsorbing the fuel vapor in an adsorbent in a canister, so that an air-fuel mixture is fed into a combustion chamber in the internal combustion engine.
(2) Description of the Related Art
A conventional evaporated fuel purge system is provided in an internal combustion engine in order to temporarily adosrb evaporated fuel, or fuel vapor evaporated in a fuel tank, in an adsorbent in a canister, and for purging the adsorbed fuel vapor in the canister into an intake passage of the internal combustion engine. This evaporated fuel purge system generally has a vapor passage connecting the fuel tank to the canister, a purge passage connecting the canister to the intake passage of the engine, and a purge control valve provided at an intermediate portion in the purge passage.
A malfunction detection apparatus for detecting a malfunction in the evaporated fuel purge system is known, for example, Japanese Laid-Open Patent Application No.2-130255 discloses such a known malfunction detection apparatus. In this conventional malfunction detection apparatus, a pressure sensor is provided in the purge passage between the canister and the purge control valve for outputting a signal indicating a flow of the air-fuel mixture in the purge passage. A malfunction in the evaporated fuel purge system can be detected by the malfunction detection apparatus in response to the signal outputted by the pressure sensor. Such malfunctions detected by the conventional apparatus include, for example, a clogging of an air inlet passage of the canister, a problem of the purge control valve, and a clogging or pipe separation of the purge passage.
However, the conventional apparatus is unable to detect a flow of air in the air inlet passage of the canister, and there is a problem in that a malfunction having occurred in the air inlet passage of the canister, or in the fuel tank, or in the canister, cannot be suitably detected by the conventional apparatus.